The invention is related to the field of underwater vehicle propulsion and maneuvering, and in particular to a system for propelling and orienting an underwater robot without the use of conventional propeller thrusters.
Since the 1990s, underwater vehicles have become a very popular approach for a number of industrial applications. For example underwater robots have played a major role in the search for undersea wrecks and in the repair of damaged underwater oil risers. Recently there has emerged a new application for such robots: industrial piping systems such as those used for the cooling cycle in nuclear reactor systems. For these applications, the robot must carry a camera or other sensor array and be able to maneuver precisely within the confines of the pipe. For these types of inspections the speed of the robot is actually quite slow. This is to ensure that the robot operator is able to carefully and thoroughly examine the images in real time.
Typical underwater robots use a set of five separate propeller thruster devices. These thrusters are driven by electric motors and have proven quite robust and useful for many applications. However, for certain applications this approach is not desirable. The large number of motors adds considerable mass and volume to the robot. In addition, thrusters exhibit nonlinearities which make them difficult to control when operating at very low speeds or when required to turn on and off rapidly. Finally, reversing the direction of a propeller (something that would be required for fine maneuvers) exerts substantial reaction moments on the body of the vehicle.